1. Technical Field
Illustrative aspects of the present invention relates to a communication terminal and a facsimile communication method for transmitting image data to a receiver (destination terminal) according to a facsimile transmission protocol in conformity with the ITU-T (International Telecommunication Union-Telecommunication Standardization Sector) recommendations, and in particular, to a communication terminal and a facsimile communication method capable of securing a “preparation time” necessary for preparing for the transmission of image data (document image) of the next page without causing a line disconnection.
2. Related Art
The T series recommendations (T.30, T.34, T.37, T.38, etc.) made by the ITU-T are widely known as an international standard of data transmission protocol between facsimile machines (an example of communication terminals). In the T series recommendations, a data transmission protocol made up of five phases (phase A-phase E) is specified as shown in FIG. 16. Ordinary facsimile machines are controlled to operate according to the data transmission protocol in order to ensure communication compatibility with receivers.
Among the T series recommendations, the recommendation T.30 specifies that an instruction signal should be transmitted to the receiver (destination terminal) repeatedly (up to three times) when no valid response signal in response to the instruction signal is received from the receiver within approximately 3 seconds (3 seconds±15%) after the transmission of the instruction signal, and the line (call) should be disconnected by transmitting a DCN (Disconnect) upon failure on the third try. This specification will hereinafter be referred to as a “communication interruption specification”. Therefore, ordinary facsimile machines are controlled to retransmit an MPS (Multi Page Signal) (as an example of the instruction signal) to the receiver when an MCF (Message Confirmation Signal) (as the response signal from the receiver) is not received within a prescribed time period T (approximately 3 seconds) after the transmission of the MPS to the receiver.
However, in a facsimile machine designed to scan a first side image (front side image, for example) and a second side image (back side image, for example) of a document by executing bidirectional feeding (inverting) of the document and transmit the scanned images (image data) of the both sides of the document to a receiver, a “preparation time” necessary for the scanning and the transmission of the second side image after the transmission of the first side image can exceed three seconds even if the document feeding is carried out at the highest speed avoiding the paper jam. Further, when the facsimile machine successively scans a plurality of documents, each document is generally reversed (i.e. fed by means of the bidirectional feeding) again after the scanning of the second side image in order to adjust the direction of the document ejected to an output tray. In such cases, a preparation time necessary for the transmission of the first side image of the next document after the transmission of the second side image of the previous (current) document can exceed three seconds, by which a timeout occurs in the receiver (due to the delay in the transmission of the first side image of the next document) and the line (call) is disconnected. Incidentally, the line disconnection due to the timeout occurs when no instruction signal (e.g. signal for transmission of data) is transmitted to the receiver within three seconds after the reception of a response signal, that is, when a “no-communication state” of the receiver after transmitting a response signal (e.g. MCF) has continued for more than three seconds (timeout period specified in the ITU-T recommendations (see the recommendation T.30)).
As a technique for preventing such a line disconnection, facsimile machines like those disclosed in Japanese Patent Provisional Publication No. 2001-8012 (hereinafter referred to as JP 2001-8012A) and Japanese Patent Provisional Publication No. HEI06-125440 (hereinafter referred to as JP HEI06-125440A) are well known. Such a facsimile machine transmits an EOM (End Of Message) signal to the receiver (for informing the receiver of a change in the transmission mode) after the completion of the transmission of the first side image. When the MCF is received from the receiver, the facsimile machine returns to the phase B and executes the facsimile communication process according to the procedures of the phase B and following phases. With such a technique, the aforementioned timeout period can be extended virtually.
Meanwhile, in Japanese Patent Provisional Publication No. SHO63-269864 (hereinafter referred to as JP SHO63-269864A), a facsimile machine which prevents the line disconnection due to the timeout by transmitting a false signal (for holding the line) to the receiver has been disclosed.
In the facsimile machines of JP 2001-8012A and JP HEI06-125440A, a time necessary for a process for establishing a data link in the phase B (included in the timeout period) is extended virtually. However, the extended time can vary depending on the state of the transmission channel (e.g. telephone circuit), the state of synchronization, and/or communication specifications such as the transmission rate (modem rate), and thus the preparation time (necessary for completing the preparation for transmitting the image of the next page) can not necessarily be secured. Further, when the transmission channel is congested and the traffic is restricted or when the transmission rate is low, the extended time gets too long and the facsimile communication takes an extremely long time even though the preparation time can be secured with ease.
Meanwhile, the facsimile machine of JP SHO63-269864A is required to execute special procedures (a process for generating the false signal, a process for transmitting the false signal, etc.) that are not specified in the ITU-T recommendations, which can cause complication of process and deterioration of versatility of the facsimile machine.